Characteristics of diode perveance and vircator output under various anode-cathode gap distances

When an electron beam is generated from a cathode, an electrode sheath plasma is also generated. Hence, the perveance of the diode is varied and changes the diode output characteristics. In our pulsed-power system "Chundoong," the perveance characteristics have been experimentally investigated, from which the sheath-plasma expansion speed has been measured to be about 3 cm//spl mu/s inside the diode. It is shown that the sheath-plasma expansion inside the diode gives the influence on the electron-beam current density. The vircator microwave output has been shown to be sensitively dependent on the anode-cathode (A-K) gap distance. The highest microwave power occurs at the initial A-K gap distance d=4 mm with peak power of 200 MW and a frequency of about 5.5 GHz in this experiment.